Network Working Group T. Talpey
Request for Comments: 5532 C. Juszczak
Category: Informational May 2009
Network File System (NFS) Remote Direct Memory Access (RDMA)
Problem Statement
Status of This Memo
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not specify an Internet standard of any kind. Distribution of this
memo is unlimited.
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Abstract
This document addresses enabling the use of Remote Direct Memory
Access (RDMA) by the Network File System (NFS) protocols. NFS
implementations historically incur significant overhead due to data
copies on end-host systems, as well as other processing overhead.
This document explores the potential benefits of RDMA to these
implementations and evaluates the reasons why RDMA is especially
well-suited to NFS and network file protocols in general.
Talpey & Juszczak Informational [Page 1]RFC 5532 NFS RDMA Problem Statement May 2009Table of Contents
1. Introduction ....................................................2
1.1. Background .................................................3
2. Problem Statement ...............................................4
3. File Protocol Architecture ......................................5
4. Sources of Overhead .............................................7
4.1. Savings from TOE ...........................................8
4.2. Savings from RDMA ..........................................9
5. Application of RDMA to NFS .....................................10
6. Conclusions ....................................................10
7. Security Considerations ........................................11
8. Acknowledgments ................................................12
9. References .....................................................12
9.1. Normative References ......................................12
9.2. Informative References ....................................13
1. Introduction
The Network File System (NFS) protocol (as described in [RFC1094],
[RFC1813], and [RFC3530]) is one of several remote file access
protocols used in the class of processing architecture sometimes
called Network-Attached Storage (NAS).
Historically, remote file access has proven to be a convenient,
cost-effective way to share information over a network, a concept
proven over time by the popularity of the NFS protocol. However,
there are issues in such a deployment.
As compared to a local (direct-attached) file access architecture,
NFS removes the overhead of managing the local on-disk file system
state and its metadata, but interposes at least a transport network
and two network endpoints between an application process and the
files it is accessing. To date, this trade-off has usually resulted
in a net performance loss as a result of reduced bandwidth, increased
application server CPU utilization, and other overheads.
Several classes of applications, including those directly supporting
enterprise activities in high-performance domains such as database
applications and shared clusters, have therefore encountered issues
with moving to NFS architectures. While this has been due
principally to the performance costs of NFS versus direct-attached
files, other reasons are relevant, such as the lack of strong
consistency guarantees being provided by NFS implementations.
Replication of local file access performance on NAS using traditional
network protocol stacks has proven difficult, not because of protocol
processing overheads, but because of data copy costs in the network